JP2005146230A - Membrane-forming stock solution and membrane for separation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane for separation, having high strength, high water permeability, high blocking property and excellent soil resistance, inexpensively and easily by using a thermoplastic resin having high chemical resistance. <P>SOLUTION: This membrane for separation is obtained by using a membrane-forming stock solution containing a thermoplastic resin, a solvent dissolving the resin, a surfactant and a substance incompatible with the solvent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a membrane-forming stock solution of a separation membrane suitable for water treatment such as drinking water production, water purification treatment, wastewater treatment, and the food industry.

  In recent years, separation membranes have been used in various fields such as water treatment fields such as drinking water production, water purification, and wastewater treatment, and food industry. In the water treatment field such as drinking water production, water purification treatment, wastewater treatment, etc., separation membranes have been used to remove impurities in water as an alternative to conventional sand filtration and coagulation sedimentation processes. In the food industry field, separation membranes are used for the purpose of separating and removing yeasts used for fermentation and concentrating liquids.

  As described above, separation membranes that are used in various ways have a large amount of treated water in the field of water treatment such as water purification treatment and wastewater treatment. If the water permeation performance is excellent, the membrane area can be reduced, and the equipment becomes compact, so that the equipment cost can be saved, which is advantageous from the viewpoint of membrane replacement cost and installation area.

  In addition, in the water purification treatment, a disinfectant such as sodium hypochlorite is added to the membrane module part for the purpose of sterilizing the permeated water and preventing biofouling of the membrane, or the membrane with acid, alkali, chlorine, surfactant, etc. In order to clean itself, the separation membrane is required to have chemical resistance.

  Furthermore, in tap water production, pathogenic microorganisms resistant to chlorine such as Cryptosporidium derived from livestock manure cannot be treated at the water purification plant, and accidents mixed into the treated water have become apparent since the 1990s. Therefore, in order to prevent such an accident, the separation membrane is required to have sufficient separation characteristics and high physical strength so that the raw water is not mixed into the treated water.

  Thus, the separation membrane is required to have excellent separation characteristics, chemical strength (chemical resistance), physical strength, stain resistance, and permeation performance. Therefore, a separation membrane using a polyvinylidene fluoride resin having both chemical strength (chemical resistance) and physical strength has been used.

  For example, in Patent Document 1, a polyvinylidene fluoride resin and various surfactants are dissolved in a good solvent to prepare a polymer solution, and the polymer solution is extruded from a die or cast on a glass plate. Subsequently, a method of forming an asymmetric porous structure by contact with a solution containing a polyvinylidene fluoride resin in a non-solvent and non-solvent-induced phase separation is disclosed. With this method, it is possible to obtain a separation membrane at a low cost, but it is difficult to achieve both a sufficient number of surface pores and a sufficiently large surface pore diameter, and it is possible to achieve both high water permeability and excellent stain resistance. It was difficult. In particular, since the polyvinylidene fluoride resin is hydrophobic, the method for producing a separation membrane by contacting with a solution containing a non-solvent such as water easily forms a dense membrane and achieves a sufficiently large surface pore diameter. It was difficult.

In relatively recent years, Patent Document 2 discloses melting and kneading inorganic fine particles and an organic liquid in a polyvinylidene fluoride resin, and extruding it from a die at a temperature equal to or higher than the melting point of the polyvinylidene fluoride resin, or pressing it with a press. And a method of forming a porous structure by cooling and solidifying, and then extracting inorganic fine particles and an organic liquid. In this method, the porosity can be easily controlled, and a macro-void can be formed and a relatively homogeneous and high-strength film can be obtained. However, if the dispersibility of the inorganic fine particles is poor, a defect such as a pinhole may occur. was there. Furthermore, this method has a drawback that the manufacturing cost is extremely high.
Japanese Patent Publication No. 1-2003 Japanese Patent No. 2899903

  In view of the above-described problems of the prior art, the present invention uses a highly chemical-resistant thermoplastic resin to produce a separation membrane having high strength, high water permeability, high blocking performance and excellent stain resistance at low cost. An object of the present invention is to provide a film-forming stock solution that can be easily manufactured.

The present invention for solving the above-described problems is achieved by the following features (1) to (7).
(1) A film-forming stock solution comprising a thermoplastic resin, a solvent for dissolving the thermoplastic resin, a surfactant, and a substance immiscible with the solvent.
(2) A film-forming stock solution containing a thermoplastic resin, a solvent that dissolves the thermoplastic resin with an octanol / water partition coefficient a, a surfactant, and a substance with an octanol / water partition coefficient b, log ₁₀ b-log ₁₀ a> 2.5
(3) The substance immiscible with the solvent or the substance having an octanol / water partition coefficient of b is selected from the group consisting of saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, higher alcohols, higher fatty acids and ethers. The film-forming stock solution as described in (1) or (2) above, which is at least one kind.
(4) The film-forming stock solution as described in any one of (1) to (3) above, wherein the thermoplastic resin is a polyvinylidene fluoride resin.
(5) The film-forming stock solution as described in any one of (1) to (4) above, wherein the viscosity is in the range of 0.01 Pa · s to 5 Pa · s.
(6) A separation membrane obtained using the membrane-forming stock solution described in any of (1) to (5) above.

  According to the membrane-forming stock solution of the present invention, a separation membrane having a sufficiently large number of surface pores and surface pore diameter can be produced inexpensively and easily, and the stain resistance is small with a decrease in water permeability due to organic matter such as humic acid. A highly reliable separation membrane can be provided. As a result, the cleaning interval of the membrane becomes longer and the filtration life becomes longer, so that the water production cost can be reduced.

  The film-forming stock solution of the present invention comprises a thermoplastic resin, a solvent that dissolves the thermoplastic resin, a surfactant, and a substance that is immiscible with the solvent that dissolves the thermoplastic resin (hereinafter referred to as immiscible substance). However, by adding a non-miscible substance together with a surfactant to the membrane forming stock solution, a separation membrane having a sufficiently large surface pore diameter can be produced inexpensively and easily. be able to.

  Although the details of this reason are unknown, it is thought to be due to the following reason. That is, in the film-forming stock solution of the present invention, the immiscible substance is solubilized or dispersed in the film-forming stock solution by the surfactant. It is considered that the surfactant is enlarged by incorporating an immiscible substance into the inside. The surfactant also acts as a pore-opening agent, and promotes the porosity of the membrane produced using the membrane-forming stock solution. Therefore, as the surfactant takes in more immiscible substances, the enlargement of the surfactant proceeds, and a large hole is formed when the stock solution solidifies.

  In order to obtain a membrane having high water permeability and excellent stain resistance, it is necessary to achieve both a sufficient number of surface pores and a sufficiently large surface pore diameter. Deteriorate. Therefore, it is necessary to control the surface pore diameter depending on the separation target, and it is controlled by the surfactant concentration, the immiscible substance concentration, and the combination of the surfactant and the immiscible substance. The concentration of the surfactant and the immiscible substance is not particularly limited, but the surfactant concentration is 0.1% by weight or more and 15% by weight or less and the immiscible substance in order to produce a film easily and inexpensively. The concentration is preferably 0.01% by weight or more and 10% by weight or less, more preferably the surfactant concentration is 1% by weight or more and 10% by weight or less, and the immiscible substance concentration is 0.1% by weight or more and 5% or less. % Weight or less is preferred.

  Further, the thermoplastic resin, the solvent for dissolving the thermoplastic resin, the surfactant and the immiscible substance are dissolved or heated at room temperature, for example, to form a film forming stock solution.

  Here, the thermoplastic resin in the present invention refers to a resin made of a chain polymer substance and having a property of being deformed / flowed by an external force when heated. Examples of thermoplastic resins include polyethylene, polypropylene, acrylic resin, polyacrylonitrile, acrylonitrile-butadiene-styrene (ABS) resin, polystyrene, acrylonitrile-styrene (AS) resin, vinyl chloride resin, polyethylene terephthalate, polyamide, polyacetal, polycarbonate , Modified polyphenylene ether, polyphenylene sulfide, polyvinylidene fluoride, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and mixtures and copolymers thereof. Among these thermoplastic resins, a polyvinylidene fluoride resin is preferable in order to obtain a separation membrane having high chemical resistance.

  The polyvinylidene fluoride resin in the present invention is a resin containing a polyvinylidene fluoride homopolymer and / or a polyvinylidene fluoride copolymer. A plurality of types of polyvinylidene fluoride copolymers may be contained. Examples of the polyvinylidene fluoride copolymer include a copolymer of vinylidene fluoride and one or more selected from tetrafluoroethylene, propylene hexafluoride, and ethylene trifluoride chloride. Further, the weight average molecular weight of the polyvinylidene fluoride resin may be appropriately selected depending on the required strength and water permeability of the separation membrane, but the strength is low when the weight average molecular weight is low, and the water permeability is high when the weight average molecular weight is high. Since it tends to be low, in order to obtain a separation membrane having both high strength and high water permeability, 50,000 to 1,000,000 is preferable. And when the workability to a separation membrane is considered, 100,000 or more and 700,000 or less are preferable, and 150,000 or more and 600,000 or less are more preferable.

  Further, the polyvinylidene fluoride resin may contain up to 50% by weight of a miscible resin. For example, the acrylic resin or cellulose ester resin is contained in a maximum amount of 50% by weight. The acrylic resin refers to a polymer compound mainly including a polymer such as acrylic acid, methacrylic acid and derivatives thereof such as acrylamide and acrylonitrile. In particular, an acrylic ester resin or a methacrylic ester resin is a polyvinylidene fluoride type. It is preferably used because of its high miscibility with the resin. The cellulose ester resin refers to a polymer compound containing an esterified cellulose such as cellulose acetate, cellulose propionate, and cellulose butyrate. The degree of esterification of the cellulose ester resin is a solvent together with the polyvinylidene fluoride resin. If it is a grade melt | dissolved in this, it will not specifically limit.

  In the present invention, the solvent that dissolves the thermoplastic resin is not particularly limited as long as it can dissolve 5 to 60% by weight of the thermoplastic resin at a temperature equal to or lower than the melting point of the thermoplastic resin. 10 to 50% by weight can be dissolved. As a solvent for dissolving this thermoplastic resin, medium chain length alkyl ketones such as cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate, Preferred are lower alkyl ketones such as esters, glycol esters and organic carbonates, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, esters and amides. Used. These solvents may be used alone or as a mixture of two or more.

  Further, as the surfactant in the present invention, it is possible to dissolve or disperse the thermoplastic resin in a solvent that dissolves the thermoplastic resin at a temperature not higher than the melting point of the thermoplastic resin described above, and solubilize or disperse the immiscible substance described later. It is not particularly limited as long as it can be used, and it is arbitrarily added within a range in which the immiscible substance can be solubilized or dispersed. Surfactants include ethylene oxides such as polyhydric alcohol esters such as sorbitan fatty acid esters, ethylene oxide low molar adducts of sorbitan fatty acid esters, ethylene oxide low molar adducts of nonylphenol, and pluronic ethylene oxide low molar adducts. Low molar adducts, polyoxyethylene alkyl esters, alkylamine salts, sodium polyacrylate, and the like are preferably used.

  Furthermore, the substance that is immiscible with the solvent that dissolves the thermoplastic resin in the present invention (immiscible substance) may have a solubility in the solvent that dissolves the thermoplastic resin of 5% by weight or less, and more preferably. It is 1% by weight or less, more preferably 0.1% by weight or less. When a thermoplastic resin, a pore-opening agent and a non-solvent described later are dissolved, the dissolving power of the solvent that dissolves the thermoplastic resin in the immiscible substance is greatly reduced. Accordingly, the immiscible substance is optionally added within a range that is solubilized or dispersed by the surfactant.

  Examples of immiscible substances include saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, higher alcohols, higher fatty acids and ethers. Examples of the saturated aliphatic hydrocarbon include pentane, hexane, heptane, octane, nonane, decane, dodecane, decalin and the like. Examples of the unsaturated aliphatic hydrocarbon include 1-pentene, 2-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and the like. Examples of the higher alcohol include 1-octanol, 2-octanol, 1-nonanol, 1-decanol, 1-dodecanol, and oleyl alcohol. Examples of higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and sardine acid. Examples of the ether include diethyl ether, dipropyl ether, diisopropyl ether and the like.

  Thus, as the immiscible substance, inexpensive saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, higher alcohols, higher fatty acids, ethers and the like are preferably used. Highly higher saturated aliphatic hydrocarbons, higher unsaturated aliphatic hydrocarbons, higher alcohols and the like are preferably used. These compounds may be used alone or as a mixture of two or more.

The miscibility between the solvent that dissolves the thermoplastic resin and the immiscible substance can be determined by using an octanol / water partition coefficient (hereinafter referred to as Pow) as one index. In general, when considering miscibility, the logarithm of the partition coefficient is used, such as log ₁₀ Pow. When the Pow of the solvent for dissolving the thermoplastic resin is a and the Pow of the immiscible substance is b, the value of log ₁₀ b-log ₁₀ a is obtained using log ₁₀ a and log ₁₀ b. The larger the value of log ₁₀ b-log ₁₀ a, the lower the miscibility of both. In the case of the present invention, it is preferable to select a solvent and an immiscible substance that dissolve the resin so as to satisfy the inequality log ₁₀ b-log ₁₀ a> 2.5, and more preferably log ₁₀ b-log _10. a> 3.0 is preferable, and log ₁₀ b-log ₁₀ a> 3.5 is more preferable.

  In addition, the octanol / water partition coefficient in this invention is calculated | required by Japanese Industrial Standard Z7260-107 (2000) "The measuring method of a partition coefficient (1-octanol / water)-Flask shaking method". The outline of this measurement method is that a certain amount of a test substance is dissolved in 1-octanol, added to two solvent phases of 1-octanol and water, mixed well, then separated into two phases, The test substance concentration is measured and the partition coefficient is obtained.

  The film-forming stock solution of the present invention contains a thermoplastic resin, a solvent that dissolves the resin, a surfactant, and a non-miscible substance. Or the like.

  The pore-opening agent is not particularly limited as long as it promotes the porosity of the membrane produced using the membrane-forming stock solution. For example, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, glycerin, etc. Inorganic salts such as polyhydric alcohols, lithium chloride, magnesium chloride and calcium chloride are preferably used.

  The non-solvent is not particularly limited as long as it is a solvent that does not dissolve the above-described thermoplastic resin and is miscible with a solvent that dissolves the thermoplastic resin. Specifically, the solubility with respect to the solvent which melt | dissolves a thermoplastic resin should just be 5 weight% or more, More preferably, it is 10 weight% or more, More preferably, 20 weight% or more is good.

  Control of phase separation by adding a non-solvent is generally performed, but if a large amount of non-solvent is added, gelation occurs or molding becomes difficult, so depending on the thermoplastic resin and the solvent in which the resin is dissolved. Therefore, it is necessary to adjust the addition amount appropriately. As the non-solvent, water, methanol, ethanol and the like are preferably used because they are inexpensive.

The separation membrane of the present invention thus produced may be a hollow fiber membrane or a flat membrane, and is selected depending on its use. The film-forming stock solution of the present invention contains four types of thermoplastic resin, a solvent that dissolves the resin, a surfactant, and an immiscible substance. The viscosity of the film-forming stock solution varies greatly depending on the concentration and combination thereof. . If the viscosity of the film-forming stock solution is too low, a film is not formed and a defect is caused or the strength of the film is lowered. Therefore, in the case of a hollow fiber membrane, the viscosity of the membrane forming stock solution is in the range of 1 Pa · s to 300 Pa · s, and in the case of a flat membrane, the viscosity of the membrane forming stock solution is in the range of 0.1 Pa · s to 10 Pa · s. It is preferable to do. More preferably, in the case of a hollow fiber membrane, it is in the range of 10 Pa · s to 200 Pa · s, and in the case of a flat membrane, it is in the range of 0.3 Pa · s to 1 Pa · s. By using a film-forming stock solution having such a viscosity, a film having high water permeability and strength can be easily obtained with a film having dimensions as described later. Further, as described later, when a polymer is coated on a support material, since the support material supplements the strength, the separation membrane itself is designed with emphasis on water permeability rather than strength. In this case, the viscosity of the membrane forming stock solution is preferably within the range of 0.01 Pa · s to 5 Pa · s in order to develop high water permeability in both the case of a flat membrane and the case of a hollow fiber membrane. Preferably in the range of 0.05 Pa · s to 3 Pa · s In the case of a hollow fiber membrane, the inner diameter is 150 μm to 8 mm, further 100 μm to 10 mm, the outer diameter is 200 μm to 12 mm, further 120 μm to 15 mm, It is preferable to design the film thickness to be in the range of 50 μm to 1 mm, more preferably 20 μm to 3 mm. The pore diameter of the inner and outer surfaces of the hollow fiber membrane can be freely selected depending on the object to be separated, but is designed to be in the range of 0.005 μm (5 nm) to 10 μm, and further 0.008 μm (8 nm) to 8 μm. Is preferred. By appropriately selecting the surfactant concentration, immiscible substance concentration, surfactant and immiscible substance concentration and combination in the film-forming stock solution of the present invention, the surface pore diameter is maintained while maintaining a sufficient number of surface pores. Can be controlled to 0.005 μm to 5 μm, and if a pore-opening agent is used, the surface pore diameter can be controlled to 0.005 μm to 10 μm.

  Further, the internal structure of the hollow fiber membrane is arbitrary, and a so-called macrovoid may exist or a homogeneous structure having pores of the same size in the film thickness direction may be used. In addition, hollow fiber fibers such as polyester, nylon, polysulfone, polyacrylonitrile, polyvinylidene fluoride, glass fibers, metal fibers, etc., which are knitted into a cylindrical shape, are coated with a polymer, and the support materials. A part of which may be impregnated with a polymer.

  On the other hand, in the case of a flat membrane, the thickness is preferably in the range of 10 μm to 1 mm, more preferably 30 μm to 500 μm. Also in the case of a flat membrane, a surface support material such as woven fabric, knitted fabric, and non-woven fabric may be coated or partially impregnated with a polymer, and in this case, the thickness including the surface support material is within the above range. Is preferred. The pore diameter on the surface can be freely selected depending on the separation target, but is preferably in the range of 0.005 μm (5 nm) to 10 μm, more preferably 0.008 μm (8 nm) to 8 μm. By appropriately selecting the surfactant concentration, the immiscible substance concentration, and the combination of the surfactant and the immiscible substance in the film-forming stock solution of the present invention, the surface pore diameter is reduced to 0 while maintaining a sufficient number of surface pores. 0.005 μm to 5 μm can be controlled, and if a pore-opening agent is used, the surface pore diameter can be controlled to 0.005 μm to 10 μm.

  The internal structure of the flat film is arbitrary, and so-called macro voids may be present or a homogeneous structure having holes of the same size in the film thickness direction may be used.

  And the separation membrane obtained using the membrane-forming stock solution of the present invention is produced, for example, by the following method. First, a thermoplastic resin, a solvent for dissolving the resin, a surfactant, and an immiscible substance are dissolved at room temperature or heated to form a film forming stock solution. Next, after the film forming solution is extruded from the die at a temperature considerably lower than the melting point of the resin, coated on a hollow fiber or cylindrical or planar support, or cast on a glass plate, A separation membrane is produced by contact with a liquid containing a non-solvent of the resin by non-solvent-induced phase separation. In addition, when a solvent that hardly dissolves the thermoplastic resin at room temperature is used as a solvent that dissolves the resin, the thermoplastic resin, the solvent that dissolves the resin, the surfactant, and the immiscible substance are dissolved at high temperature. A membrane-forming solution is produced, and after the membrane-forming solution is discharged from the die, a separation membrane is produced by a heat-induced phase separation method in which the membrane is cooled to cause phase separation and solidification.

  The separation membrane of the present invention thus obtained is housed in a casing having a raw solution inlet and a permeate outlet and used as a membrane module. When the membrane module is a hollow fiber membrane, bundle a plurality of hollow fiber membranes and store them in a cylindrical container, and fix both ends or one end with polyurethane or epoxy resin so that the permeate can be collected. Alternatively, both ends of the hollow fiber membrane are fixed in a flat plate shape so that the permeate can be collected. When the separation membrane is a flat membrane, the flat membrane is wound around in an envelope shape around the liquid collection tube and wound into a spiral shape and stored in a cylindrical container so that the permeate can be produced. Flat membranes are arranged on both sides to fix the periphery in a watertight manner so that the permeate can be collected.

  The membrane module is used as a liquid separation device for forming water by providing at least a pressurizing means on the stock solution side or a suction means on the permeate side. A pump may be used as the pressurizing means, or a pressure due to a water level difference may be used. Moreover, what is necessary is just to utilize a pump and a siphon as a suction means.

  The water permeability of the membranes in the examples and comparative examples were measured as follows.

When the membrane is a hollow fiber membrane, a miniature module having a length of 200 mm consisting of four hollow fiber membranes is prepared, and the water permeation rate of pure water is measured under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa. 50 kPa) (Q0, unit = m ³ / m ² · h). Next, a 20 ppm aqueous solution of humic acid (reagent, manufactured by Wako Pure Chemical Industries, Ltd.) is filtered to 2 m ³ / m ² by total external pressure filtration under conditions of a filtration differential pressure of 16 kPa and a temperature of 25 ° C. Further, permeated water is supplied for 1 minute at a backwash pressure of 150 kPa, and the pure water permeation amount immediately after that is measured (Q1). A = Q1 / Q0 is used as an index of stain resistance.

  When the membrane is a flat membrane, it is cut into a circle with a diameter of 50 mm, set in a cylindrical filtration holder, and the other operations are the same as those for the hollow fiber membrane.

The number of surface pores of the separation membrane is obtained by taking a photograph using a scanning electron microscope and counting the number of observed pores. The photo of the scanning electron microscope is taken at a magnification of 50,000 times. The surface pore diameter of the separation membrane is determined by measuring the diameters of 20 arbitrary pores from the same scanning electron microscope photograph and calculating the average. When the pore is elliptical, the minor axis a and the major axis b are measured, and (a × b) ^0.5 is taken as the equivalent circular diameter. In this case, the surface pore diameter is the average of the equivalent circular diameters of 20 arbitrary pores.
<Example 1>
25% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 64% by weight of dimethylformamide (log ₁₀ Pow = −0.87), polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Chemical Co., Ltd., trade name) 5% by weight of Ionette T-20C), 3% by weight of decane (log ₁₀ Pow = 5.98) and 3% by weight of water were mixed and dissolved at a temperature of 95 ° C. to form a film-forming stock solution (viscosity: 10 Pa · s) was prepared. The membrane-forming stock solution was discharged from the die while accompanying a 50% by weight aqueous solution of dimethylformamide as a hollow portion forming liquid, and solidified in a coagulation bath comprising a 50% by weight aqueous solution of dimethylformamide at a temperature of 20 ° C. to produce a hollow fiber membrane. . The difference in log ₁₀ Pow between dimethylformamide and decane was 6.85.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.05 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 2.45 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 2.30 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1. Moreover, the scanning electron micrograph image | photographed when calculating | requiring the surface pore diameter of a hollow fiber membrane is shown in FIG.
<Example 2>
A membrane-forming stock solution (viscosity: 10 Pa · s) was prepared in the same manner as in Example 1 except that decane was changed to hexane (log ₁₀ Pow = 3.61), and a hollow fiber membrane was produced in the same manner. The difference in log ₁₀ Pow between dimethylformamide and hexane was 4.48.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.05 μm. The pure water permeation rate at 50 kPa and 25 ° C. was 2.22 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 2.15 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 3>
25% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 61% by weight of dimethylformamide, 5% by weight of T-20C, 3% by weight of decane, 3% by weight of lithium chloride and 3% by weight of water A film-forming stock solution (viscosity: 20 Pa · s) was prepared by mixing and dissolving at a temperature of 95 ° C. The membrane-forming stock solution was discharged from the die while accompanying a 50% by weight aqueous solution of dimethylformamide as a hollow portion forming liquid, and solidified in a coagulation bath comprising a 50% by weight aqueous solution of dimethylformamide at a temperature of 20 ° C. to produce a hollow fiber membrane. . The difference in log ₁₀ Pow between dimethylformamide and decane was 6.85.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.2 μm. The pure water permeability at 50 kPa and 25 ° C. was 2.60 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 2.45 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Comparative Example 1>
A membrane-forming stock solution (viscosity: 10 Pa · s) was prepared in the same manner as in Example 1 except that decane was not added to the membrane-forming stock solution and the weight percent thereof was dimethylformamide, and a hollow fiber membrane was produced in the same manner. .

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.023 μm. The pure water permeation rate at 50 kPa and 25 ° C. was 2.20 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.55 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1. Moreover, the scanning electron micrograph image | photographed when calculating | requiring the surface pore diameter of a hollow fiber membrane is shown in FIG.
<Comparative example 2>
A membrane-forming stock solution (viscosity: 20 Pa · s) was prepared in the same manner as in Example 3 except that decane was not added to the membrane-forming stock solution and its weight% was changed to dimethylformamide, and a hollow fiber membrane was produced in the same manner. .

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.03 μm. The pure water permeability at 50 kPa and 25 ° C. was 2.30 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.60 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 4>
13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 76% by weight of dimethylacetamide (log ₁₀ Pow = 0.77), 5% by weight of T-20C, 3% by weight of decane and water A film-forming stock solution (viscosity: 1 Pa · s) was prepared by mixing and dissolving at a temperature of 95 ° C. at a rate of 3 wt%. The difference in log ₁₀ Pow between dimethylacetamide and decane was 5.21.

  Next, after the film-forming stock solution is cooled to 25 ° C., it is applied to a polyester cylindrical support having an outer diameter of 1730 μm and an inner diameter of 900 μm. A hollow fiber membrane in which a porous membrane was formed on the surface of a polyester cylindrical support was prepared by immersing it in hot water three times and washing it.

The obtained hollow fiber membrane had an outer diameter of 1.8 mm, an inner diameter of 0.9 mm, and an average pore diameter of 0.05 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 1.12 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.03 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 5>
A membrane-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 4 except that decane was changed to hexane, and a hollow fiber membrane was produced in the same manner. The difference in log ₁₀ Pow between dimethylacetamide and hexane was 2.84.

The obtained hollow fiber membrane had an outer diameter of 1.8 mm, an inner diameter of 0.9 mm, and an average pore diameter of 0.05 μm. The pure water permeability at 50 kPa and 25 ° C. was 1.04 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.94 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Comparative Example 3>
A membrane-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 4 except that decane was changed to hexanol, and a hollow fiber membrane was produced in the same manner. The difference in log ₁₀ Pow between dimethylacetamide and hexanol was 1.26.

The obtained hollow fiber membrane had an outer diameter of 1.8 mm, an inner diameter of 0.9 mm, and an average pore diameter of 0.02 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 1.03 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.80 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.

Under the condition of log ₁₀ b-log ₁₀ a = 1.26 <2.5, the stain resistance against the humic acid aqueous solution could not be improved.
<Comparative example 4>
A membrane-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 4 except that decane was not added to the membrane-forming stock solution and the weight percent was changed to dimethylacetamide, and a hollow fiber membrane was produced in the same manner. .

The obtained hollow fiber membrane had an outer diameter of 1.8 mm, an inner diameter of 0.9 mm, and an average pore diameter of 0.02 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 1.00 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.74 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 6>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. This resin solution was discharged from the die while accompanying γ-butyrolactone as a hollow portion forming liquid, and solidified in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to prepare a base hollow fiber.

Next, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 76% by weight of N-methyl-2-pyrrolidone (log ₁₀ Pow = −0.11), 5% by weight of T-20C, A film-forming stock solution (viscosity: 1 Pa · s) was prepared by mixing and dissolving decane at 3 wt% and water at 3 wt% at a temperature of 95 ° C. This membrane-forming stock solution was uniformly applied to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane in which a porous membrane was formed on the surface of the base hollow fiber. The difference in log ₁₀ Pow between N-methyl-2-pyrrolidone and decane was 6.09.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.05 μm. The pure water permeability at 50 kPa and 25 ° C. was 1.05 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.99 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 7>
A base hollow fiber was produced in the same manner as in Example 6.

A membrane-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 4 except that decane was changed to oleyl alcohol (log ₁₀ Pow = 3.5), and this membrane-forming stock solution was uniformly applied to the surface of the base hollow fiber. And hollowed immediately in a water bath to produce a hollow fiber membrane having a porous membrane formed on the surface of the base hollow fiber. The difference in log ₁₀ Pow between N-methyl-2-pyrrolidone and oleyl alcohol was 3.61.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.08 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 1.10 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.05 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 8>
A base hollow fiber was produced in the same manner as in Example 6.

Next, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 73% by weight of N-methyl-2-pyrrolidone, 5% by weight of T-20C, 3% by weight of decane, 3% of lithium chloride A film-forming stock solution (viscosity: 5 Pa · s) was prepared by mixing and dissolving 3% by weight of water and water at a temperature of 95 ° C. This membrane-forming stock solution was uniformly applied to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane in which a porous membrane was formed on the surface of the base hollow fiber. The difference in log ₁₀ Pow between N-methyl-2-pyrrolidone and decane was 6.09.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.2 μm. The pure water permeation rate at 50 kPa and 25 ° C. was 1.26 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.17 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 9>
A base hollow fiber was produced in the same manner as in Example 6.

Subsequently, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 73% by weight of N-methyl-2-pyrrolidone, 5% by weight of T-20C, 3% by weight of decane, and a weight average molecular weight of 2 A film-forming stock solution (viscosity: 1 Pa · s) was prepared by mixing and dissolving 3% by weight of polyethylene glycol at 3% by weight and 3% by weight of water at a temperature of 95 ° C. This membrane-forming stock solution was uniformly applied to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane in which a porous membrane was formed on the surface of the base hollow fiber. The difference in log ₁₀ Pow between N-methyl-2-pyrrolidone and decane was 6.09.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.1 μm. The pure water permeation rate at 50 kPa and 25 ° C. was 1.22 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.10 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 10>
A base hollow fiber was produced in the same manner as in Example 6.

A film-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 1 except that T-20C was replaced with polyoxyethylene sorbitan monostearate (Sanyo Kasei Co., Ltd., trade name Ionette T-60C). This membrane-forming stock solution was uniformly applied to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane in which a porous membrane was formed on the surface of the base hollow fiber. The difference in log ₁₀ Pow between N-methyl-2-pyrrolidone and decane was 6.09.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.05 μm. The pure water permeability at 50 kPa and 25 ° C. was 1.16 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 1.05 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Comparative Example 5>
A base hollow fiber was produced in the same manner as in Example 6.

  A film-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 6 except that decane was not added to the film-forming stock solution and its weight% was changed to N-methyl-2-pyrrolidone. Was applied uniformly to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane having a porous membrane formed on the surface of the base hollow fiber.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.02 μm. The pure water permeability at 50 kPa and 25 ° C. was 0.75 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.51 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Comparative Example 6>
A base hollow fiber was produced in the same manner as in Example 10.

  A film-forming stock solution (viscosity: 1 Pa · s) was prepared in the same manner as in Example 10 except that decane was not added to the film-forming stock solution and its weight% was changed to N-methyl-2-pyrrolidone. Was applied uniformly to the surface of the base hollow fiber and immediately solidified in a water bath to produce a hollow fiber membrane having a porous membrane formed on the surface of the base hollow fiber.

The obtained hollow fiber membrane had an outer diameter of 1.4 mm, an inner diameter of 0.8 mm, and an average pore diameter of 0.02 μm. The pure water permeation rate at 50 kPa and 25 ° C. was 0.70 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 0.47 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 11>
13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 76% by weight of dimethylacetamide, 5% by weight of T-20C, 3% by weight of decane and 3% by weight of water at 95 ° C. A film-forming stock solution (viscosity: 0.3 Pa · s) was prepared by mixing and dissolving at a temperature.

Next, after the film-forming stock solution is cooled to 25 ° C., it is applied to a non-woven fabric made of polyester fiber having a density of 0.48 g / cm ³ and a thickness of 220 μm. Immediately after application, it is immersed in pure water at 25 ° C. for 5 minutes. Further, the film was immersed in hot water at 80 ° C. three times for washing to obtain a flat film. The difference in log ₁₀ Pow between dimethylacetamide and decane was 5.21. The average pore diameter of the obtained flat membrane was 0.05 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 6.66 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeation rate was 6.20 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Example 12>
A film-forming stock solution (viscosity: 0.3 Pa · s) was prepared in the same manner as in Example 11 except that decane was changed to heptane (log ₁₀ Pow = 4.66), and a flat membrane was produced in the same manner. The difference in log ₁₀ Pow between dimethylacetamide and heptane was 3.89. The average pore diameter of the obtained flat membrane was 0.04 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 6.48 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 6.10 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.
<Comparative Example 7>
A film-forming stock solution (viscosity: 0.3 Pa · s) was prepared in the same manner as in Example 11 except that decane was not added to the film-forming stock solution and its weight% was changed to dimethylacetamide. did.

The average pore diameter of the obtained flat membrane was 0.02 μm. The pure water permeation amount at 50 kPa and 25 ° C. was 6.35 m ³ / m ² · h (Q0).

The aqueous humic acid solution was filtered to ² m ³ / m ² under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and backwashed. The pure water permeability was 5.35 m ³ / m ² · h (Q1). The evaluation results are summarized in Table 1.

  Separation membranes produced by the membrane-forming stock solution of the present invention can be used in water treatment fields such as water purification, water treatment, wastewater treatment, industrial water production, river water, lake water, groundwater, seawater, sewage, Waste water or the like can be treated water.

2 is a scanning electron micrograph of the outer surface of a hollow fiber membrane produced by the method of Example 1. FIG. 2 is a scanning electron micrograph of the outer surface of a hollow fiber membrane produced by the method of Comparative Example 1.

Claims (6)

  A film-forming stock solution comprising a thermoplastic resin, a solvent for dissolving the thermoplastic resin, a surfactant, and a substance immiscible with the solvent. A film-forming stock solution containing a thermoplastic resin, a solvent that dissolves the thermoplastic resin with an octanol / water partition coefficient of a, a surfactant, and a substance with an octanol / water partition coefficient of b, the inequality log ₁₀ b A film-forming stock solution satisfying -log ₁₀ a> 2.5.   The solvent immiscible substance or the substance having an octanol / water partition coefficient b is at least one selected from the group consisting of saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, higher alcohols, higher fatty acids and ethers. The film-forming stock solution according to claim 1 or 2, wherein   The said thermoplastic resin is a polyvinylidene fluoride resin, The film forming undiluted | stock solution in any one of Claims 1-3 characterized by the above-mentioned.   Viscosity is in the range of 0.01 Pa · s to 5 Pa · s, the film-forming stock solution according to any one of claims 1 to 4.   A separation membrane obtained using the membrane-forming stock solution according to claim 1.